It seems kinda odd to me that a disconnected drive disaster recovery would be considered undefined behavior for a storage appliance - that's the whole point of having a software RAID so that you're able to gracefully recover from a disaster such a something as simple as a cable failure.
That being said, I will definitely test this - from previous replies it sounded like it would require a reboot, which apparently it does not. I would think if my HBA supports hot-swap and it's able to detect my JBOD when it's unplugged and plugged back in (which it does), then FreeNAS *should* be able to as well. I do think it's a realistic expectation that there would be data corruption, but that's outside of FreeNAS' control and I respect that.
And with that I'm guessing that our needs fall outside of the abilities of FreeNAS. This has all been extremely helpful as I'll still need to keep this system running for the next year or so, but ultimately I'm finding that FreeNAS can't (and really isn't meant to) provide the continuous up-time that we require - it's looking like a clustered storage is what we need.
I work on TrueNAS HA daily (got my own test system too) and I can tell you that a SAS cable failure *will* trigger a failover, so uptime is maintained.
For FreeNAS, its harder to determine how to recover from a disconnected cable. If you are looking for reliability from failed cabling, there is a solution... multipathing. SAS multipathing was designed specifically to address issues like this. If you don't have or don't support that functionality, you might be able to online the disks with zpool online commands. I've never tried to do that before, so I'm not sure how well it would work.
As for power supply getting unplugged, you should have dual redundant power supplies to avoid that kind of issue as well.
I will agree that probably 90% of FreeNAS users have a single large pool, but 10% is still a lot of users (by numbers) with more than 1 zpool.
If you are in a RAID10 environment, I'd simply do stripes of disks that are in different jbods. You lose one jbod and you only lose 1 of every 2 disks in all of the vdevs. I've had customers deliberately do this.
Also, I'm not sure what controller you are using right now, but all of the 6Gb and 12Gb SAS cards I've worked with seem to handle disconnecting and reconnecting of jbods, disks, etc with hotswap and hotplugging working just fine. I've only seen the 12Gb SAS on more recent versions of FreeNAS though, so if you're using a version from 2016 you will be outside of my experience base.